Yarn feeder with adjustable braking device

ABSTRACT

Device to feed yarn to machines making use thereof, particularly the weft yarn (T) to gripper or projectile looms, of the type in which the yarn to be feed is unwound from a reserve (R) wound on a drum onto the outlet end of which, where a first yarn deviation takes place, there acts a brake device (FR) which is centered on the drum axis and adjustable along the same, upstream of an outlet yarn guide where a second yarn deviation takes place. The brake device (FR) comprises a frustoconical braking element with continuous surface and differentiated elasticity, carried by a stiff ring support to which it is fixed close to its major circumference, and the stiff ring support is mounted so as to oscillate about two axes (S1, S2) which are perpendicular one in respect of the other and both in respect of the axis of the drum.

FIELD OF THE INVENTION

The present invention concerns devices to feed yarn to machines makinguse thereof, and particularly a weft yarn feeder for gripper orprojectile loons having improved characteristics.

BACKGROUND OF THE INVENTION

It is well known to feed yarn to machines making use thereof,particularly the weft yarn to looms, by means of feeding devices or yarnfeeders. Such devices are positioned between the spool and the loom andare meant to temporarily store the weft yarn. They also facilitate itsunwinding from the spool, and subsequently feed it to the loom insertionmembers with optimal and preset yarn tension values.

The type of structure universally adopted at present for such feedingdevices involves winding the yarn into successive turns around a windingunit or drum, kept motionless, by means of a winding arm moved by anelectric motor. Means for detecting the amount or reserve of yarnpresent on the winding drum are provided to control the running androtation speed of the motor of the feeding device according to theamount of yarn drawn by the loom; so as to make the yarn unwinding speedfrom the spool as uniform as possible.

When yarn feeders are used on gripper or projectile looms, they compriseat their outlet end yarn braking means, positioned downstream of theyarn winding drum and meant to feed the weft yarn to the loom with aspecific desired tension. Many of the known yarn braking devices actdirectly on the outlet end of the drum and are positioned upstream of anoutlet yarn guide of the feeder, meant to ensure a correct unwinding ofthe weft yarn.

Most yarn feeders make use of brake devices consisting of a plurality ofnatural or synthetic bristles, fixed to a support in the form of aclosed ring carried by a bracket movable along the main axis of the yarnfeeder. The plurality of bristles bear--with a variable pressure adaptedto be preset by adjusting the axial position of the bracket--onto theouter periphery of the yarn reserve winding drum of the feeder.

Other yarn braking devices have been conceived, as an alternative to theones with bristles: and their use has proved advantageous to overcomethe drawback of the rapid wear of the bristles. The braking element inthese devices comprises a plurality of thin sheet-metal strips,positioned side-by-side onto a frustoconical surface and pressing ontothe outlet end of the feeder drum. To guarantee--by a self-adjustment ofthe strips--an efficient and continuous-contact of the strips with thewinding drum, the said braking element is preferably mounted onto acup-shaped support with open bottom, carried by a bracket of the yarnfeeder the position of which is adjustable along the drum axis. A yarnbraking device with sheet-metal strips of this type, which has provedsatisfactory and has found a widespread use, is disclosed in EP-B1-49897filed by the same Applicant. In this brake device, the sheet-metalstrips are in the form of thin blades and the cup-shaped support ismounted on the movable bracket of the yarn feeder by way of a doublearticulation, so as to be able to perform limited oscillations about twoaxes perpendicular to each other and to the axis of the feeder drum.

More recently, brake devices for yarn feeders having still differentcharacteristics have been conceived. These devices comprise a continuousbraking band carried by a plurality of tongues with varying flexibility.The tongues are self-adjustable in that they are mounted movable into afixed support. Examples of such brake devices are described inPCT/EP93/03086 and PCT/EP93/03262, both filed by the same Applicant. Dueto the particular configuration of these devices and, above all, totheir mounting--which allows the braking element to be widely deformedand to perform short movements in every direction in the support (thusacting like a universal joint, adapted to guarantee all degrees offreedom)--a perfect adjustment of the braking element in respect of thedrum is obtained in the tangent area of contact, particularly takinginto account the deformations caused by the passage of the weft yarn,and this allows to guarantee a very regular yarn tension diagram.

Even further improvements in the behavior of the brake device, in itsarea of contact with the feeder drum--allowing to simultaneously obtaina yarn tension trend, during weft insertion, with no harmful peaks (soas to ensure a good result in the weft insertion process)--have beenaccomplished with the yarn braking device proposed by the Applicant inPCT/EP94/00476. In this case the device, centered on the drum axis andadjustable along the same, comprises a frustoconical braking elementwith continuous surface and varying flexibility, carried by a stiff ringsupported to which it is fixed close to its major circumference. Thesupport is in turn fixedly mounted onto a bracket of the yarn feeder,the position of which is adjustable along the drum axis. Similar brakedevices--wherein the braking element consists of a continuous surfacesupported by a highly flexible member, such as to allow aself-adjustment of the continuous surface in respect of the outlet endof the winding drum--are described in EP-A1-534263 in the name of L.G.L.Electronics.

From a careful consideration of the techniques described heretofore andtheir developments, it can be noticed that brake devices for yarnfeeders have evolved towards the use of a braking element withcontinuous surface, which seems to be more suited than others to solvethe more and more complicated problems faced by the experts as a resultof the advanced state of technique in this field and its constantprofess.

It can be noticed moreover that the already known types of brake devicesfor yarn feeders: including the most evolved ones, while allowing toobtain a satisfactory braking effect for weft yarn insertion purposes,are not adapted to conveniently solve the problem of the properadjustment of the braking element in respect of the outlet end of thewinding drum, when--as it happens fairly often, for various reasons, inthe industrial production process--in the brake devices which areintroduced on the market (either new, or after a more or less longperiod of use): the braking element is not perfectly aligned with thewinding unit of the yarn feeder.

SUMMARY OF THE INVENTION

The object of the present invention is to supply a yarn feeder, whereinthe brake device--while providing the advantageous characteristicsresulting from the use of the latest types of braking elements(particularly, a frustoconical braking element with continuous surface,carried by a stiff ring support centered on the drum axis and adjustablealong the same)--can be more easily adapted to any of the possibleaforementioned misalignments, so as to allow, on one hand, to make thebest use of yarn feeders produced with high precision and, on the otherhand, to be able to produce yarn feeders having less characteristics ofprecision, with the certainty that they can equally be used for a verylong time, with acceptable performances.

For this purpose, the present invention provides a device to feed theyarn to machines making use thereof, particularly the weft yarn togripper or projectile looms, of the type in which the yarn to be fed isunwound from a reserve wound on a drum, onto the outlet end ofwhich--where a first yarn deviation takes place--there acts a brakedevice, which is centered on the drum axis and adjustable along thesame, upstream of an outlet yarn guide--where a second yarn deviationtakes place--characterized in that, the brake device comprises afrustoconical braking element with continuous surface and varyingelasticity, carried by a stiff ring support to which it is fixed closeto its major circumference, and in that, the stiff ring support ismounted so as to oscillate about two axes, which are perpendicular onein respect of the other and both in respect of the drum axis.

A brake device according to the present invention, thanks to thecharacteristic combination of the particular structure and shape of thebraking element, with its mounting system comprising a doublearticulation allows a prompt and easy adjustment of the braking surfaceof the element to the best conditions of tangency in respect of the endportion of the winding unit, even if the winding Unit and the brakedevice are not perfectly coaxial. The brake device is therefore adaptedto solve any problems due to a geometrically imperfect constructionand/or mounting of the yarn feeder.

According to a preferred embodiment, the stiff ring support is hinged atthe ends of a fork pivoted to a slide, the position of which cap beadjusted along the drum axis.

The invention will now be described in further detail, by mere way ofexample, with reference to a preferred embodiment thereof, illustratedon the accompanying drawings, in which:

FIG. 1 is a side view, with some cutaway parts, of the improved yarnfeeder according to the invention;

FIG. 2 is a detailed front view of the brake device mounted on the yarnfeeder shown in FIG. 1, from which some parts have been removed; and

FIG. 3 is a diagrammatic view of a detail of the brake device shown inFIG. 2.

BRIEF DESCRIPTION OF THE DRAWINGS

As shown in FIG. 1, the yarn feeder AT according to the inventionreceives in known manner the yarn F from a reel B or spool and feedssaid yarn as weft T to a stripper or projectile loom (not shown).

Also in known manner, in the yarn feeder AT which comprises a body 1with an arm 1A projecting there from a reserve R of yarn F is wound intosuccessive turns, by a winding element 2, around a drum 3 keptmotionless and the axis of which is parallel to the arm 1A.

The weft yarn T is fed to the loom by being unwound along the drum axisfrom the reserve R, guided by an outlet yarn guide 4, after having beenbraked in correspondence of the outlet end of the drum 3.

The yarn guide 4 is carried--downstream of the drum 3 and centered alongits axis--by a bracket 4A: the position of which is adjustable along theupper arm 1A of the yarn feeder AT.

In the aforedescribed yarn feeder, the braking of the weft yarn T at theoutlet end of the drum 3 is obtained by means of a brake device FRcomprising a braking element 5, which consists of an annular elasticmembrane extending over a frustoconical surface and being fixed, withits outer edge of wider diameter: to a stiff ring 6. According to theinvention, the stiff ring 6 is carried by the arm 1A of the yarn feederAT with a double articulation system comprising a fork 7, onto the endsof which the ring 6 is pivoted in 7A, and a slide 8 on which the fork 7is pivoted in 8A. The slide being movable along the arm 1A to allowregulating the contact pressure of the braking element 5 onto the outletend of the drum 3.

As shown more clearly in FIG. 2, which is a front view of the yarnfeeder without the bracket 4A and yarn guide 4 the fork 7 engages thering 6 in correspondence of two hingeing points 7A positioned along ahorizontal axis S1, while the fork 7 is in turn mounted on the slide 8by way of the hinge 8A positioned on the vertical axis S2. The axes S1and S2 are thus perpendicular one in respect of the other and they areboth perpendicular to the axis of the yarn feeder.

The mounting system with double articulation enables the stiff ring 6,supporting the braking element 5, to perform oscillating movements abouttwo axes S1 and S2, so as to allow the braking element which has afrustoconical surface, to take up the most correct tangent position inrespect of the outlet end portion of the drum 3, normally just incorrespondence of the point of contact with the drum having apseudo-toroidal surface.

FIG. 3 shows in detail a section of the brake device FR according to apreferred embodiment thereof. The device consists of a stiff ring 6 andof a substantially frustoconical braking element 5 fixed thereto. Thebraking element 5 is formed by a continuous elastic membrane, preferablywith varying elasticity, mainly thanks to the presence of a bent endportion 5A close to the stiff ring 6, comprising, on the inner surfaceof its other free end portion, a wearproof metal element 9, which isalso formed with a strictly continuous frustoconical surface and whichextends tangentially to the outlet end portion of the drum 3.

We claim:
 1. Device for feeding weft yarn to gripper or projectilelooms, comprising a drum for storing a weft yarn reserve wound on thedrum, said drum having an axis and an outlet end, said weft yarn beingunwound from said weft yarn reserve onto said outlet end where a firstyard deviation takes place, a yarn brake device acting on said outletend, said yarn brake device being positioned upstream of an outlet yarnguide where a second yarn deviation takes place, said yarn brake devicebeing centered on the drum axis and adjustable along said axis, saidyarn brake device comprising a frustoconical braking element having amajor circumference and a minor circumference, and a continuous surfaceof varying elasticity, said braking element being fixed to a stiff ringsupport close to said major circumference, and said stiff ring supportbeing mounted so as to oscillate about two axes, which are perpendicularone in respect of the other, and both in respect of the axis of thedrum.
 2. Device according to claim 1, wherein said stiff ring support ishinged at ends of a fork pivoted to a slide, the position of said slideadapted to be adjustable along the axis of the drum.